This should be more properly called Village on the Cheap, but there is no limit to the basic question:

How would a settlement for a decent number of people look like, if it was built out of the very cheap, and often simple technologies, that still offer a lifestyle comparable to today's standards?

Many of these concepts were designed for refugee camps, and as temporary shelters, but they have the potential to serve for permanent living, with all the comforts (some assembly may be required). Due to cost and other reasons are decentralized structures preferred.

This is a work in progress. One more advanced study is the Hexayurt Country. Additionally, Open Source Ecology are developing machines to provide for a modern civilisation on a village level.

Requirements and Assumptions

What do we assume for this concept to work? We will make the job relatively easy for us, but we can eventually drill down to the details, and see how other environments impact the 'City'. So what does the city have:

first off, sufficient space; that should be easy

there is abundant fresh water - not the same as drinking water

a climate where composting toilets work, which excludes the subarctic and other cold places

small amount of firewood to augment the solar cookers

Things left out for now:

medical services

education

transportation inside of the 'city'

initial import of materials and resources

larger organizational structures (states)

Hospitals and schools depend a lot on available budget. A start to solving these topics is train people to deal with the common cases at a neighborhood level to take the load off. The rest is out of scope here, or to be covered later.

Household On The Cheap

The basic unit of living, one household can be quite self-sufficient.

In terms of cost:

A hexayurt-type house itself is $300 - $1200 per unit. It could be available under $500 in materials suitable for 20+ years of use in non-hurricane climates, and more like $1000 in hurricane-resistant materials.

per house it's $200 for the solar cooker, the stove, the solar panels, the lights, the batteries and the housing for the shitbucket toilet infrastructure unit. Probably less, but $200 is safe.

This cuts the start up costs for essential services a long, long way. Means your initial population can give it a go for, say, $2,000 of survival infrastructure per household, plus a bit more for whatever tools they need to earn a living.

Assuming 4 people living in a household, and 100 people (small village), makes $50,000. 1000 people makes it $500,000. Not that much for something semi-permanent.

Energy

devices powered by simple sources like AA batteries or hand crank; also solar and wind power

all day solar charger

lighting with efficient light sources

backing up by more conventional means as generators? (more likely a last resort)

Water

transported in by trucks

solar water pasteurization and/or other means (have shiny silver huts arranged as people see fit, with *small* - $100 or even smaller - solar panels on the roof, water delivered in five gallon buckets by pickup truck)

in modern households can the demand climb up to 200 liters per day; more conservative estimates speak in figures of 5 liters of drinkable (or distilled) water per day; and 20+ liters of otherwise useful water (both numbers can be pushed down even more, depending on the equipment and willingness of the inhabitants)

Groups/Clusters of Households

Certain key pieces of equipment are productive enough to supply several households at once, or too expensive/energy consuming for one. The size of such a 'cluster' will depends on the resources that need sharing. (While it is out of scope here, this also means potential for conflict.)

fast chargers powered by a large solar panel

transport of water

will every house need their toilet? What about other amenities (bathrooms, showers, etc)?